Methods for Producing Biomass-Based Fuel With Pulp Processing Equipment

ABSTRACT

A method for mitigating the costs of establishing a biomass-based pellet manufacturing plant includes identifying an existing pulp processing plant, obtaining permission to access and convert the pulp processing plant, and converting the pulp processing plant for manufacture of biomass-based pellets. Converting the pulp processing plant may include installing a pellet mill in the pulp processing plant, re-routing output from a pulp digester, such that the output enters the pellet mill, and bypassing unnecessary equipment. Biomass-based pellets may be manufactured in the converted pulp processing plant by liberating lignin from biomass-based feedstock via pulp digester and pelletizing the biomass-based feedstock and the liberated lignin to form the biomass-based pellets.

RELATED APPLICATION

This application claims the benefit of the filing date and priority to U.S. Provisional Application 61/152,556, filed Feb. 13, 2009, the entirety of which is hereby incorporated by reference.

BACKGROUND

The present disclosure relates to processing energy resources, and, more particularly, to methods for producing biomass-based fuel with pulp processing equipment.

Biomass of various types may be used to manufacture densified fuel. Biomass may take the form of wood, woody biomass, or other biomass such as, without limitation, sugarcane bagasse, straw, switchgrass, or other agricultural material where biomass may be a byproduct of other processes or where biomass may be a feedstock grown for the purpose of making directly or indirectly, a fuel.

The terms “pellets” and “briquettes” commonly refer to fragments of biomass, treated biomass, coal, or some or all in combination that have been compacted to form a densified fuel produced in various sizes and shapes. For example, various size feedstocks, such as sawdust or chips ranging in size from less than 1″ to over 3″ along the longest dimension, may be processed and pelletized. Material may be dried and extruded through dies sized for the desired cross-sectional area and of varying lengths. Floor-mounted machines or presses with dyes may receive prepared feedstock and discharge extruded pellets sized (e.g., by cutting or trimming) to desired lengths at the outlet of the machines or presses. The term “white pellet” may refer to the use of suitably sized and pelletized wood that has had minimal if any treatment beyond chipping and grinding prior to being introduced into the pellet machine or press. White pellets may be used in residential heaters, in district heating, and/or in industrial power generation, including coal-fired power generation plants.

Industrial use of white pellets may be limited by the white pellets' inherent properties including sensitivity to water, low hardness, and lack of durability, leading to the production of dust as the pellets abrade through handling and/or as a result of moisture absorption. These properties, independently and together, may cause the pellets to rapidly disintegrate. Due to such limitations, white pellets require specific storage and handling accommodations to protect the pellets from the elements and to mitigate dust concentrations that may create an explosion hazard. Consequently, using white pellets in coal-fired power generation plants in concentrations from 1% to 100% may require significant adaptations to both plant operating procedures and capital equipment considering, for example, that coal may be typically stored and handled outdoors with exposure to the elements.

The term “black pellet” may refer to a pellet with a lignin binder and/or coating induced by processing the biomass feedstock prior to introducing the biomass into the pellet machine or press. Steam explosion may be used in manufacturing densified fuel as a means to free lignin from cellular structures of biomass, thereby allowing the lignin to commingle with the fiber portion of the biomass and, when compacted by the pellet machine or press, forming both a waterproof or water-resistant internal binder as well as a waterproof or water-resistant protective surface coating that enhances the durability of pellets and briquettes. As a result, pellets and briquettes may have improved abrasion properties and may be stored outdoors in a manner similar to outdoor storage of coal. Having physical characteristics similar to coal may facilitate the introduction of pellets into coal handling processes of conventional coal plants, resulting in both capital cost and operating cost savings as compared to the use of white pellets.

Providing a manufacturing and processing plant for densified biomass-based fuel poses a number of challenges for the energy industry. These challenges may entail complications and expenses including one or more of the purchase and preparation of land, coordination with governmental zoning restrictions and other regulations, coordinating expectations with a surrounding community, design and construction of facilities, design and assembly of complex equipment and procedures, purchase of new equipment, and, generally, large upfront expenses in time, capital and other resources. Therefore, it may be desirable to have methods that mitigate the challenges associated with manufacturing and processing densified biomass-based fuel.

SUMMARY

The present disclosure relates to processing energy resources, and, more particularly, to methods for producing biomass-based fuel with pulp processing equipment.

In one embodiment, a method of manufacturing biomass-based pellets includes liberating lignin from biomass-based feedstock via pulp digester. The method may include pelletizing the biomass-based feedstock and the liberated lignin to form the biomass-based pellets.

In one embodiment, a method for converting a pulp processing plant to a biomass-based pellet manufacturing plant includes installing a pellet mill in the pulp processing plant. The method may include re-routing output from a pulp digester, such that the output enters the pellet mill and bypassing unnecessary equipment.

In one embodiment, a method for mitigating the costs of establishing a biomass-based pellet manufacturing plant includes identifying an existing pulp processing plant, obtaining permission to access and convert the pulp processing plant, and converting the pulp processing plant for manufacture of biomass-based pellets.

The features and advantages of the present disclosure will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features.

FIG. 1 illustrates a block diagram indicating a method of mitigating the costs of establishing a biomass-based pellet manufacturing plant in accordance with certain embodiments of the present invention.

FIG. 2 illustrates a block diagram indicating a method for converting a pulp processing plant to a biomass-based pellet manufacturing plant in accordance with certain embodiments of the present invention.

FIG. 3 illustrates a block diagram indicating a converted pulp processing plant in accordance with certain embodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates to processing energy resources, and, more particularly, to methods for producing biomass-based fuel with pulp processing equipment. For purposes of this disclosure, a biomass-based pellet may include without limitation a fragment or piece of any shape, size, or division, including a briquette. A biomass-based pellet, and biomass-based material may include, at least in part and without limitation, material consisting of or derived from wood, woody biomass, or any other biomass such as bamboo, sugarcane bagasse, straw, switchgrass, husks, or other agricultural material where biomass may be a byproduct of other processes or where biomass may be a feedstock grown for the purpose of manufacturing a fuel.

In certain embodiments of the present disclosure, existing pulp making, papermaking, and/or cellulosic ethanol equipment may be used to produce biomass-based exploded or otherwise treated product that may be ready for densification to achieve a biomass-based pellet. In some instances, this type of pellet is called a “high-density” or “black” pellet. In certain embodiments of the present disclosure, existing technology, e.g., equipment widely used for preprocessing wood in the pulp and paper industry, may be adapted to accomplish the liberation of lignin present in biomass-based feedstock. An existing pulp processing plant may be used with some or all equipment intact and, with the addition of pelletizing equipment, may produce a steam-exploded biomass-based pellet without building new steam explosion facilities. Conversion of conventional pulp processing plant digestion technology may be adapted to so that chemical treatment, which may be typical to pulping processes, may not be necessary in a converted pulp processing plant. Existing equipment may be converted to steam explosion equipment and coupled with densification processes to manufacture biomass-based pellets.

Referring now to FIG. 1, in one exemplary embodiment, the costs associated with establishing biomass-based pellet manufacturing may be reduced by first identifying 100 an existing pulp processing plant. This identification may include researching several pulp processing plants and determining whether any of them is in financial distress and/or in need of financial stimulation. In some embodiments, the existing pulp processing plant may be a paper mill, a freestanding pulp processing facility, or any other pulp processing source.

Once an existing pulp processing plant has been identified 100, permission 105 may be obtained to access and convert the pulp processing plant to a biomass-based pellet manufacturing facility. This permission 105 may be obtained through contract agreement, purchase of assets, merger, acquisition, lease agreement, or any other grant of rights to access and conversion, including altering intended use of an asset already owned.

Once an existing pulp processing plant has been identified 100 and permission 105 obtained, it may be converted 110 for manufacture of biomass-based pellets. This conversion 110 is described in detail below with reference to FIG. 2.

In some embodiments, costs may be further reduced by identifying 115 an existing source of biomass-based feedstock, before, after, or in conjunction with identification 100 of pulp processing plant. Some examples of sources of biomass-based feedstock may include nearby forests, grasslands, or any of a number of other renewable biomass-based feedstock sources. After identification 115 of an existing source of biomass-based feedstock, permission 120 may be obtained to access and use the biomass-based feedstock for manufacture of biomass-based pellets. This permission 120 may be obtained through contract agreement, purchase of assets, merger, acquisition, lease agreement, or any other grant of rights to access and use, including altering intended use of an asset already owned. If the existing source of biomass-based feedstock is remote from the pulp processing plant, an additional step of obtaining permission 125 to transport the biomass-based feedstock from the existing source to the pulp processing plant may be included either in addition to, or in place of the step of obtaining permission to access and use the biomass-based feedstock. For example, this permission may include a contract for purchase of goods, including quantities requirements and term of contract provisions.

Referring now to FIG. 2, in one exemplary embodiment, a pulp processing plant may be converted for use in biomass-based pellet manufacturing. Such a conversion may involve converting 200 an existing pulp digester for use in the manufacture of biomass-based pellets, installing 205 a pellet mill in the pulp processing plant, re-routing 210 output from the pulp digester, such that the output enters the pellet mill, and/or bypassing 215 unused components in the pulp processing plant.

Converting 200 an existing pulp digester may involve removal of some or all equipment used for chemical treatment and/or lignin removal. Installing 205 a pellet mill may involve leasing, purchasing, or otherwise acquiring a pellet mill of the type described below with reference to FIG. 3, and ensuring that it is delivered to the pulp processing plant for installation in a location suitable for use with the rest of the equipment useful for biomass-based pellet manufacture. Re-routing 210 the output from the pulp digester may not require physical changes to equipment, and may be as simple as moving a conveyor, or may involve complex movements of equipment. In some instances, re-routing 210 the output from the pulp digester may include re-routing and/or bypassing intermediate equipment, such as, for example, a blow tank. Bypassing 215 unused components may include bypassing particular equipment useful in pulp processing plant operations but unnecessary in biomass-based pellet manufacture. When bypassed equipment is unnecessary, the method may further include removing 220 and/or selling 225 the bypassed equipment.

Referring now to FIG. 3, converted pulp processing plant 300 is illustrated in accordance with certain embodiments of the present disclosure. Biomass-based feedstock may be collected from a location near converted pulp processing plant 300. For example, biomass-based feedstock may be timber collected from forestland adjacent to converted pulp processing plant 300. Alternatively, biomass-based feedstock may be delivered to pulp processing plant 300 from a remote location. For example, biomass-based feedstock may be bamboo grown in another country and delivered to pulp processing plant 300, either intact, or pre-processed to some extent. Any of a number of other sources for biomass-based feedstock may also be suitable. Depending on the source and condition of the biomass-based feedstock, it may undergo additional treatment in existing facilities 305 prior to entry into pulp digester 325. Existing facilities 305 may include any number and variety of existing papermaking and/or cellulosic ethanol production equipment. For example without limitation, existing facilities 305 may include one or more of storage yard 310, debarking equipment 315, chipping equipment 320, pulp digester 325, and blow tank 330, which may or may not be coupled together by any conveying equipment or other means of transferring material. Depending on the particular biomass-based feedstock, one or more of the units of existing facilities 305 may be modified or even omitted.

Upon delivery to converted pulp processing plant 300, biomass-based feedstock may be stored in storage yard 310 for some time prior to use. Storage yard 310 may be a location, with certain equipment if desired, adapted for one or more of receiving, storing, and preparing biomass-based material for processing. In some embodiments, storage yard 310 is a wood yard suitable for use with wood-based materials.

Depending on the type of biomass-based feedstock, it may pass through debarking equipment 315, which may be any equipment and/or machinery configured to prepared biomass-based material for further processing by removing material, for example, by removing bark from surfaces of logs.

Biomass-based feedstock may pass through flume shower 360 or other equipment suitable to wash off dirt or other impurities in biomass-based feedstock, when using unprocessed biomass-based feedstock. Flume shower 360 may be part of existing facilities 305, or flume shower 360 may be added to existing facilities 305 for use in biomass-based pellet manufacture. In some instances, flume shower 360 may be modified or omitted, depending on the particular application.

If the size of biomass-based feedstock is larger than desirable for use in pulp digester 325, it may pass through chipping equipment 320 prior to entry into pulp digester 325. Chipping equipment 320 may be any equipment and/or machinery configured to reduce biomass-based material into smaller parts. In some instances, a grinder (not shown) may be used for further reduction in size of biomass-based feedstock.

Biomass-based feedstock may pass through dryer 365, if desired, to reduce moisture content to a level suitable for use in pulp digester 325. For example, dryer 365 may be used to obtain moisture content between 0% and 15% by weight. Dryer 365 may be a rotary dryer, steam dryer, superheated steam dryer, low temperature dryer, or any of a number of other devices for adjusting moisture content.

Existing pulp processing plants may typically use pulp digester 325 in a cooking process, along with significant amounts of chemicals and/or enzymes sometime referred to as “cooking liquor.” The cooking process may be used to separate lignin and/or sugars from fiber and maintain separation in dilute slurry. The lignin and fiber are typically moved to separate vessels in existing pulp processing plants, with no further comingling of fiber and lignin. In some embodiments of converted pulp processing plant 300, chemicals and/or enzymes may be added to biomass-based feedstock in a chemical treatment operation (not shown) to produce a biomass-based slurry for use in pulp digester 325. In other embodiments, chemicals and enzymes may be omitted.

Biomass-based feedstock (or slurry) may enter pulp digester 325 through an opening sized accordingly. Pulp digester 325 may include any vessel and associated equipment configured to receive biomass-based feedstock (or slurry) and process it under desired pressures and at desired temperatures. Pulp digester 325 may include one or more vessels configured to operate in a batch manner, in a multi-batch or semi-continuous manner, or in a continuous manner. Examples of other existing pulp digesters 325 may include, but are not limited to, Masonite guns, standard Kraft digesters, standard sulfite digesters, chemithermomechanical pulping, thermomechanical pulping, groundwood pulping, and pressurized groundwood pulping.

If the operation is batch-type, the supply of biomass-based feedstock (or slurry) may cease and the pulp digester 325 may be closed off. In a continuous operation, the supply of biomass-based feedstock (or slurry) may be continuous. At a predetermined temperature and temperature, pulp digester 325 will, over a predetermined amount of time, treat or cook the biomass-based feedstock (or slurry), using steam, either with or without chemical additives and/or water, to liberate lignin from the biomass-based feedstock by steam explosion. Once the cooking is suitably complete, pulp digester 325 may be opened to adjacent blow tank 330, allowing removal of cooked biomass-based material, which includes the biomass-based feedstock and the liberated lignin, from pulp digester 325 via explosion into blow tank. Cooked biomass-based material may transferred to the blow tank 330 on a batch and/or continuous basis. Blow tank 330 may include any vessel and associated equipment configured to receive treated, or cooked biomass-based material, which may be in a slurry state with cooking liquor and/or steam, from pulp digester 325.

Existing pulp processing plants may not be designed to use such pulping technologies to steam explode fibers, but may be designed to use pulping technologies under various conditions. For example, pulping technologies may involve pressures below 150 psi (pounds per square inch), chemical additives, one or more cooking processes, and a dilute slurry that may comprise approximately 50% dry solids.

Conventional high-density pellet manufacturing, on the other hand, typically involves higher temperatures and pressures and smaller chambers than pulp digester 325. Operating pressures may exceed 150 psi in certain implementations, such as where a Masonite gun may be employed, where operating pressures may reach or exceed 1,000 psi. Thus, in certain instances, converted pulp processing plant 300 may employ longer cook times than found in conventional high-density pellet manufacturing.

Steam explosion may be used at normal operating pressures to soften biomass-based fibers in preparation for re-entry at atmospheric conditions, thus exploding the fibers at a lower pressure or, in the case of a Masonite gun, a significantly higher pressure. Certain embodiments may accomplish steam explosion at pressures in approximate ranges of 225 psi to 375 psi and/or may produce a product of 85% to 92% dry solids, while keeping lignin with fiber for pellet processing. Steam impregnating raw fuel may pre-soften the material. Certain embodiments may use chemicals with the steam impregnation to further soften or accelerate softening raw fiber prior to cooking. Such chemicals may include sodium sulfite, caustic soda, or any other suitable chemical, as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure. Other embodiments may include addition of supplementary lignin and/or omit steam explosion from the process of liberating lignin.

Cooked biomass-based material may pass from blow tank 330 through dryer 370, if desired, to reduce moisture content to a level suitable for use with pelletizing equipment 340. For example, dryer 370 may be used to obtain moisture content between 0% and 15% by weight. Dryer 370 may be a rotary dryer, steam dryer, superheated steam dryer, or any of a number of other devices for adjusting moisture content.

Cooked biomass-based material may be transferred, either directly, or via one or more of blow tank 330 and dryer 370, from pulp digester 325 to pelletizing equipment 340, which may include one or more of a pellet mill 345, pellet cooling equipment 350 and pellet storage 355. Cooked biomass-based material may be processed by pellet mill 345 to form biomass-based pellets. Pellet mill 345 may be any device suitable for extrusion or other compression of cooked biomass-based material to create biomass-based pellets. After exiting pellet mill 345, biomass-based pellets may pass through or otherwise encounter pellet cooling equipment 350 for cooling. Pellet cooling equipment 350 may be any equipment or means for cooling biomass-based pellets, including, but not limited to, air circulation or water quenching. In some embodiments, pellet cooling equipment 350 may not be needed, and biomass-based pellets may be cooled during storage. Biomass-based pellets may then be stored at pellet storage 355. Because high-density biomass-based pellets are moisture and abrasion resistant, pellet storage 355 may be, for example, indoor storage, outdoor storage, covered storage, or uncovered storage. Additionally biomass-based pellets may be used in standard coal handling equipment, including railcars, conveyors, storage, and other processing facilities, eliminating the need for significant capital investment in order to coal fire biomass-based pellets with coal.

In addition to existing facilities 305, a typical existing pulp processing plant may include balance of the existing plant 335, which may constitute equipment that may not be needed in manufacturing and processing biomass-based pellets. Balance of the existing plant 335 may be removed or left in place, as desired or as needed to accommodate pellet equipment 340.

As would be appreciated by one of ordinary skill in the art having the benefit of the present disclosure, any number of modifications, adaptations, and alternatives may be employed to convert an existing pulp processing plant. For example, “steam” may refer not only to water vapor, but may also include other vapors useful in the applications indicated above.

Thus, the methods disclosed herein provide the potential for significantly lowering costs of producing biomass-based fuel and initiating large-scale manufacturing and processing of biomass to make biomass-based feedstock for power generation units such as cogeneration, boilers and other types of power plants. Conversion of existing pulp processing plants according to the present disclosure offers significant economies compared to new construction of high-pressure steam explosion. Methods according to the present disclosure may be applied to existing pulp and feedstock production sites in any number of various wood and pulp and paper countries to facilitate business related to manufacturing, processing and delivering biomass-based fuel. Other technical advantages will be apparent to those of ordinary skill in the art in view of the specification, claims, and drawings.

Therefore, the present disclosure is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present disclosure. In addition, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. 

1. A method of manufacturing biomass-based pellets comprising: liberating lignin from biomass-based feedstock via pulp digester; and pelletizing the biomass-based feedstock and the liberated lignin to form the biomass-based pellets.
 2. The method of manufacturing biomass-based pellets of claim 1, wherein steam explosion is absent from the liberating and the pelletizing.
 3. The method of manufacturing biomass-based pellets of claim 1, comprising adding supplementary lignin.
 4. The method of manufacturing biomass-based pellets of claim 1, comprising adding chemicals.
 5. The method of manufacturing biomass-based pellets of claim 4, wherein the chemicals comprise sodium sulfate, caustic soda and combinations thereof.
 6. The method of manufacturing biomass-based pellets of claim 1, wherein the pulp digester has been converted for use in the manufacture of biomass-based pellets.
 7. The method of manufacturing biomass-based pellets of claim 6, comprising introducing a biomass-based slurry into a vessel of the pulp digester through a chemical treatment operation; ceasing supply of the biomass-based slurry to the pulp digester; allowing the biomass-based slurry to cook in the pulp digester for a predetermined period of time at a predetermined temperature, creating a cooked biomass-based material; removing the cooked biomass-based material from the pulp digester; delivering the cooked biomass-based material from the pulp digester to a pellet mill; and pelletizing the cooked biomass-based material to form biomass-based pellets.
 8. The method of manufacturing biomass-based pellets of claim 6, comprising continuously introducing a biomass-based slurry into a vessel of the pulp digester through a chemical treatment operation; allowing the biomass-based slurry to cook in the pulp digester for a predetermined period of time at a predetermined temperature, creating a cooked biomass-based material; continuously removing the cooked biomass-based material from the pulp digester; delivering the cooked biomass-based material from the pulp digester to a pellet mill; and pelletizing the cooked biomass-based material to form biomass-based pellets.
 9. A method for converting a pulp processing plant to a biomass-based pellet manufacturing plant, comprising: installing a pellet mill in the pulp processing plant; re-routing output from a pulp digester, such that the output enters the pellet mill; and bypassing unnecessary equipment.
 10. The method for converting a pulp processing plant to a biomass-based pellet manufacturing plant of claim 9, comprising removing the bypassed equipment.
 11. The method for converting a pulp processing plant to a biomass-based pellet manufacturing plant of claim 9, comprising: converting the pulp digester for use in the manufacture of biomass-based pellets.
 12. The method for converting a pulp processing plant to a biomass-based pellet manufacturing plant of claim 11, wherein converting the pulp digester comprises: removing equipment used for lignin removal.
 13. The method for converting a pulp processing plant to a biomass-based pellet manufacturing plant of claim 12, wherein converting the pulp digester comprises: removing equipment used for chemical treatment.
 14. A method for mitigating the costs of establishing a biomass-based pellet manufacturing plant, comprising: identifying an existing pulp processing plant; obtaining permission to access and convert to the pulp processing plant; converting the pulp processing plant for manufacture of biomass-based pellets.
 15. The method for mitigating the cost of establishing a biomass-based pellet manufacturing plant of claim 14, comprising: identifying an existing source of biomass-based feedstock near the pulp processing plant; obtaining permission to access and use the biomass-based feedstock for manufacture of biomass-based pellets.
 16. The method for mitigating the cost of establishing a biomass-based pellet manufacturing plant of claim 14, comprising: identifying an existing source of biomass-based feedstock; obtaining permission to transport the biomass-based feedstock from the existing source to the pulp processing plant. 